During the course of normal embryonic development, the fetal testis produces Mullerian Inhibiting Substance (MIS), which causes the involution of the Mullerian ducts in the male. Understanding the chemical nature and biological action of MIS will provide insight into the complex control of normal sexual differentiation and congenital anomalies of the urogenital system. Additionally, since a number of tumors require fetal antigens and therefore become susceptible to fetal control mechanisms, the potential role of MIS as a regressor of tumors of Mullerian duct anlage (endometrium and cervix of the uterus) may be investigated. An abundant source of MIS is available since it is known that the neonatal calf testis continues to produce this glycoprotein, most probably by Sertoli cells. The techniques to be used in this study include: (1) isolation of viable calf Sertoli cells; (2) study of the parameters of MIS secretion by maintaining calf Sertoli cells in tissue culture; (3) detection of de novo synthesis of MIS by these cells, using a combination of radioactive amino acid and fucose incubations; (4) separation and characterization of labelled MIS using gel filtration chromatography and polyacrylamide gel electrophoresis; (5) positive identification of MIS using a reliable organ culture bioassay system for the detection of the presence of this molecule and (6) effects of various metabolic substances on the secretion of MIS by studying the kinetics of MIS production and inhibition in Sertoli cell cultures in the presence of gonadotropins, cAMP, and other compounds.